select()函数使用

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#define MYPORT 1234    // the port users will be connecting to
#define BACKLOG 5     // how many pending connections queue will hold
#define BUF_SIZE 200

int fd_A[BACKLOG];    // accepted connection fd
int conn_amount;    // current connection amount

void showclient()
{
    	int i;
    	printf("client amount: %d\n", conn_amount);
    
   	for (i = 0; i < BACKLOG; i++) 
    	{
        	printf("[%d]:%d  ", i, fd_A[i]);
    	}
    	printf("\n\n");
}


int main(void)
{
    	int sock_fd, new_fd;  // listen on sock_fd, new connection on new_fd
    	struct sockaddr_in server_addr;    // server address information
    	struct sockaddr_in client_addr; // connector's address information
    	socklen_t sin_size;

    	int yes = 1;
    	char buf[BUF_SIZE];
    	int ret;
    	int i;

    	if ((sock_fd = socket(AF_INET, SOCK_STREAM, 0)) == -1)
    	{
        	perror("socket");
        	exit(1);
    	}

    	if (setsockopt(sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) 
    	{
        	perror("setsockopt");
        	exit(1);
    	}

    	server_addr.sin_family = AF_INET;         // host byte order
    	server_addr.sin_port = htons(MYPORT);     // short, network byte order
    	server_addr.sin_addr.s_addr = INADDR_ANY; // automatically fill with my IP
    	memset(server_addr.sin_zero, '\0', sizeof(server_addr.sin_zero));
    
    	if (bind(sock_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) 
    	{
        	perror("bind");
        	exit(1);
	}

	if (listen(sock_fd, BACKLOG) == -1)
	{	
		perror("listen");
		exit(1);
	}

	printf("listen port %d\n", MYPORT);
	fd_set fdsr;
	
	int maxsock;
	struct timeval tv;
	conn_amount = 0;
	sin_size = sizeof(client_addr);
	maxsock = sock_fd;

	while (1) 
	{
		// initialize file descriptor set
		FD_ZERO(&fdsr);
		FD_SET(sock_fd, &fdsr);

		// timeout setting
		tv.tv_sec = 30;
		tv.tv_usec = 0;
		// add active connection to fd set
		for (i = 0; i < BACKLOG; i++)
		{
			if (fd_A[i] != 0)
			{
				FD_SET(fd_A[i], &fdsr);
			}
		}

		ret = select(maxsock + 1, &fdsr, NULL, NULL, &tv);
		if (ret < 0)
		{
			perror("select");
			break;
		}
		else if (ret == 0)
		{	
			printf("timeout\n");
			continue;
		}
		// check every fd in the set
		for (i = 0; i < conn_amount; i++)
		{
			if (FD_ISSET(fd_A[i], &fdsr))
			{
				ret = recv(fd_A[i], buf, sizeof(buf), 0);
				if (ret <= 0) 
				{// client close
					printf("client[%d] close\n", i);
					close(fd_A[i]);
					FD_CLR(fd_A[i], &fdsr);
					fd_A[i] = 0;
				}
				else
				{// receive data
					if (ret < BUF_SIZE)
						memset(&buf[ret], '\0', 1);
					printf("client[%d] send:%s\n", i, buf);
				}
			}
		}
		// check whether a new connection comes
                if (FD_ISSET(sock_fd, &fdsr))
		{
			new_fd = accept(sock_fd, (struct sockaddr *)&client_addr, &sin_size);
			if (new_fd <= 0)
			{
				perror("accept");
				continue;
			}
			// add to fd queue
			if (conn_amount < BACKLOG)
			{
                        	fd_A[conn_amount++] = new_fd;
                        	printf("new connection client[%d] %s:%d\n", conn_amount,
                        	inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));

                        	// 贴这段代码 重点是这两句  关系到select的第一个参数
                        	//
				if (new_fd > maxsock)
					maxsock = new_fd;
			}
                        else 
                        {
                            printf("max connections arrive, exit\n");
                            send(new_fd, "bye", 4, 0);
                            close(new_fd);
                            break;
                        }
		}
                showclient();
	}
            
	// close other connections
	for (i = 0; i < BACKLOG; i++) 
	{
		if (fd_A[i] != 0) 
		{
			close(fd_A[i]);
		}
	}
	exit(0);
}